The present invention refers to a hydraulic binder with a quick setting time for use in cement compositions, comprising a clinker which contains calcium fluoroaluminate 11CaO.7Al2O3.CaF2, (hereafter abbreviated as C11A7f), sodium aluminate, optionally sodium bicarbonate, and lime which has not undergone the baking process of clinker.
In the present text the following abbreviations are used:
CaOxe2x95x90C; Al2O3xe2x95x90A; SiO2xe2x95x90S; CaF2xe2x95x90f; Fe2O3xe2x95x90F;
11CaO.7Al2O3.CaF2xe2x95x90C11A7f; 12CaO.7Al2O3xe2x95x90C12A7;
3CaO.Al2O3xe2x95x90C3A; CaO.Al2O3xe2x95x90CA; 3CaO.SiO2xe2x95x90C3S;
2CaO.SiO2xe2x95x90C2S; (2CaO.Fe2O3-6CaO.2Al2O3.Fe2O3)ssxe2x95x90C4AF where ss signifies solid solution
3CaO.3Al2O3.CaSO4xe2x95x90C4A3S
For various types of application such as rapid fixing and repairs on concrete and masonry vertical and horizontal surfaces it is important that cement materials having very quick setting time are available. Examples of such applications are: placing of manhole covers in roads, fixing steel brackets, plumbing pipes and hinges, laying dummy wooden and metal frames, laying electrical boxes and sheathing for electrical plants, wooden dowels, sealing of cement conduits, sewers or cisterns, blocking weak water leaks in underground structures, basements and elevator pits.
Further examples of uses are: paving landing runways, covering roofs, mortar or concrete casting in tunnels and subways, lining slopes and slanting grounds and increasing productivity by reducing formworks removal time in plants for the manufacture of concrete products, such as: blocks, pipes, panels, cross beams and structural uprights.
Other uses consist in accelerating the setting and hardening time of mortar and concrete, premixed concrete and cement binders.
Therefore, modified Portland-type binders have been developed, which have faster setting and hardening characteristics than normal Portland cement.
According to the Italian M.D. (Ministerial Decree) dated Aug. 31, 1972 xe2x80x9cNorme sui requisiti di accettazione e modalità di prova degli agglomerati cementizi e delle calci idraulichexe2x80x9d (=Regulations for acceptance requirements and test methods for cement agglomerates and hydraulic limes), the quick setting binders must nave a minimum initial setting time greater than 1 minute, final setting time below 30 minutes, determined on standard compounds, and must moreover have a minimum resistance to compressive stress after 7 days of at least 13 MPa. Further specifications regard the content of SO3 (lower than 3,5%), and MgO (lower than 4%).
The xe2x80x9cso calledxe2x80x9d rapid binders are characterized in general by high contents of calcium aluminate. Among the aluminates , C12A7, and in a smaller amount, C3A, hydrate very quickly, while CA hydrates slowly. The rate of hydration can be modified by the presence of salt or chemical products which act as accelerators or retardants.
Various rapid binders are obtained by xe2x80x9cclinkerizationxe2x80x9d of mineral mixes or industrial by-products followed by grinding of the resulting clinker, and addition of additives such as anhydrite. Various types of clinker are known for rapid binders, such as:
a) Clinker enriched in C12A7, the composition thereof falling in the compatibility tetrahedron C2Sxe2x80x94Cl2A7xe2x80x94C3Axe2x80x94C4AF. These types of cements are sold under the name of Prompt Vicat.
b) Clinker containing fluorinated derivatives of C12A7, whose composition falls in the compatibility tetrahedron C3Sxe2x80x94C2Sxe2x80x94C11A7fxe2x80x94C4AF, like the Regulated Set Cement used in the USA and Giesereibinder in Heidelberg.
c) Clinker containing calcium sulphoaluminate C4A3S e xcex2-C2S. The baking temperature in this case is more critical as compared with clinker a) and b) because the stability range of C4A3S is rather narrow: 1150 and 1350xc2x0 C.
d) Mixes of Portland cement and aluminous cement.
The b) types of clinker that result in improved products resistance characteristics due to the presence of C3S, and in addition permit recycling (by incorporating into the clinker) of alumina bearing scoria, which is sold at inexpensive market rates. Fluoroaluminate cements were developed in the early 70""s (Italian patent no. 37815 A/69 and Italian patent no. 988018).
Similar cement compositions were successively developed in Japan, and sold under the name Jet Cement. DE 2163604 claims clinkers containing from 40% to 60% of C11A7f and from 30% to 50% of C3S.
Clinker containing fluoroaluminate can be used advantageously in preparing quick setting binders, nonetheless, as can be deduced from the results shown in DE 2163604, in order to achieve satisfactory resistance to compressive stress, elevated contents of C11A7f are required, equal to at least 40% in weight of the clinker. This is an unquestionable drawback, given the relevant increase in the costs of the final product due to the high quantity of alumina (Al2O3) and calcium fluoride necessary for the preparation of the clinker.
The European Patent Application EP-A-819660 described a quick hardening cement wherein the clinker contains calcium fluoroaluminate and lime which has not undergone the baking process of the clinker (xe2x80x9craw limexe2x80x9d). The use of this highly reactive type of lime allows to obtain a quick setting cement without the use of high quantities of C11A7f.
Nonetheless, the setting times of cements described in EP-A-819660, vary considerably with the ambient temperature at which the cement is used. Thus, while the hardening values at moderate or elevated ambient temperatures are good, those at low temperatures are less satisfactory. The reduction in hardening rate is an evident disadvantage, above all in the event of its use in countries with cold climates, or during cold seasons.
Differences in hardening times due to temperature makes it necessary to modify the cement composition according to seasonal climate, with the obvious disadvantage that working with the product is more complex and less flexible.
In consideration of the drawbacks stated above, the need is felt for new quicker-hardening concretes, particularly for use at cold temperatures.
In addition, it is desirable to obtain quick-hardening cements having an increased constancy in hardening times throughout the entire temperature range in which it is used.
Object of the present invention is a hydraulic binder for cement compositions comprising a clinker containing calcium fluoroaluminate 11CaO.7Al2O3.CaF2, sodium aluminate, lime added to clinker after baking, and optionally sodium bicarbonate. Such binder permits the formation of cement compositions that have a very quick hardening time at both high and low temperatures.
These cement compositions have the further advantage of an elevated setting time stability throughout the temperature range 5xc2x0 C.-35xc2x0 C.
The binder of the invention is prepared by grinding the above mentioned ingredients together with clinker, or by grinding them separately and then mixing them with the previously ground clinker.
The invention comprises, in addition, premixed dry compositions containing said binder that are suitable for preparing quick-setting cement mixes, such as mortar and concrete, and their use in the building industry.